Narayanankutty Pariyadath

Preparations and properties of tripodal and linear tetradentate N,S-Donor ligands and their complexes containing the MoO22+core

Abstract New linear and tripodal tetradentate ligands, LH 2 , are reported and their syntheses are described. The new linear ligands L = HSCH 2 CH 2 SCH 2 CH 2 NRCH 2 CR 2 SH, R = H, CH 3 ) and the new tripodal ligands N(CH 2 CH 2 SH) 2 CH 2 Z, Z = CH 2 NH 2 , CH 2 N(CH 3 ) 2 , CH 2 N(C 2 H 5 ) 2 , CH 2 SCH 3 and CO 2 - were synthesized. The known linear ligands HSCH 2 CH 2 NCH 3 (CH 2 ) n NCH 3 CH 2 CH 2 SH (n = 2, 3) and HSCR 2 CH 2 NHCH 2 CH 2 NHCH 2 CR 2 SH (R = H, CH 3 ) were also utilized. These ligands react with MoO 2 (acac) 2 in CH 3 OH to yield MoO 2 L complexes in high yield. Infra-red and 1 H nmr spectra provide evidence to supplement X-ray crystallographic results reported elsewhere for selected numbers of the series. Octahedral structures with cis MoO 2 2+ groupings are assigned. Solution 1 H nmr studies are consistent with a trans placement of the two thiolate donors in agreement with the X-ray studies.

EPR ligand superhyperfine interactions in mononuclear Mo(V) complexes: Implications for Mo enzymes

Abstract Reaction of Mo2O4(S2CNEt2)2 or Mo2O4(S2PPr2i)2 with thiol-containing ligands leads to the preparation of mononuclear Mo(V) complexes which display EPR absorption. For example, Mo2O4(S2CNEt2)2 reacts with o-NH2·C6H4·SH to yield Mo(S2CNEt2)(S·C6H4·NH)2. In a like manner Mo(S2CNEt2)(NR·C6H4·S)2 (R = D, Me), Mo(S2CNEt2)(S·C6H4· S)2 and Mo(S2PPr2i)(NH·C6H4· S)2 were prepared. Mo(S2CNEt2)(NH·C6H4· S)2 displays an EPR spectrum with superhyperfine splitting from 14N (2.4 G) and 1H (7.4 G). EPR spectra of the N-methyl and N-deutero complexes confirm these assignments. The anion [Mo(NH·C6H4·S)3]− generated in situ from Mo(NH·C6H4·S)3 shows A( 1 H ) 6.4 and A( 14 N ) 2.1 G. Splitting from 31P is seen in the dithiophosphinato complexes Mo(S2PPr2i)(NH·C6H4·S)2 and MoO(S2PPr2i)(O·C6H4·S). Variable temperature studies are required for the maximum resolution of ligand superhyperfine structure. The ligand splittings are qualitatively correlated with the symmetry of the orbital bearing the unpaired electron. These results show that substantial 1H superhyperfine splitting is possible for protons on coordinated ligands and establish the feasibility of a similar assignment for proton splittings in Mo enzymes.